The Boat Race has been labelled "possibly the most dramatic in history" after a Thames swimmer brought it to a halt and a rower was taken to hospital.

The event was stopped and restarted after Trenton Oldfield swam into the path of the vessels, narrowly avoiding the blade of an Oxford oar.

The 35-year-old was pulled from the river and taken away on a police launch before being arrested on suspicion of a public order offence.

Cambridge powered on to victory, but not without further drama: a clash of oars led to Oxford crew member Hanno Wienhausen breaking his blade, allowing the Light Blues to pull clear.

Celebrations were then muted as Oxford bowman Alexander Woods was taken to hospital after collapsing in his boat at the end of the race. The 27-year-old Pembroke College student was later said to be in a stable condition.

Oldfield, dressed in a wetsuit, created the unprecedented disruption when he was spotted close to the boats between the two and three-mile marker while the crews were neck and neck.

Police have not named the swimmer but said a man was being detained on suspicion of a section 5 public order offence, namely behaviour likely to cause harassment, alarm or distress. A spokesman said: "He is currently in custody at a west London police station while inquiries into the circumstances are carried out."

Oldfield studied contemporary urbanism at the London School of Economics and has a website called Elitism Leads to Tyranny, which discusses civil disobedience tactics.

Karl Hudspith, president of the Oxford University Boat Club, blamed the swimmer for ruining his crew's big day, writing on Twitter: "My team went through seven months of hell, this was the culmination of our careers and you took it from us."

The contest ended with no presentation ceremony and the Boat Race Company described it as "possibly the most dramatic in Boat Race history".